Baryon Acoustic Oscillations and the Hubble constant: past, present and future

Abstract

We investigate constraints on the Hubble constant (H 0 ) using Baryon Acoustic Oscillations (BAO) and baryon density measurements from Big Bang Nucleosynthesis (BBN). We start by investigating the tension between galaxy BAO measurements and those using the Lyman-α forest, within a Bayesian framework. Using the latest results from eBOSS DR14 we find that the probability of this tension being statistical is 6.3%. We measure H 0 = 67.6±1.1 km s −1 Mpc −1 , with a weak dependence on the BBN prior used, in agreement with results from Planck Cosmic Microwave Background (CMB) results and in strong tension with distance ladder results. Finally, we forecast the future of BAO + BBN measurements of H 0 , using the Dark Energy Spectroscopic Instrument (DESI). We find that the choice of BBN prior will have a significant impact when considering future BAO measurements from DESI.

The BAO+BBN take on the Hubble tension

“…In section 2 we will introduce our BAO and BBN data sets, as well as the direct H 0 measurements and CMB data that we use for comparison. In the results section 3, we will first attempt to confirm the results of Cuceu et al [31] assuming a minimal ΛCDM cosmology. However, we will use both primordial deuterium and helium measurements, and we will rely on an improved treatment of primordial abundances -in particular, a well-motivated theoretical error on BBN predictions.…”

“…Essentially, this amounts in taking different assumptions on the most important nuclear rates. Cuceu et al [31], performed a similar test and found that their results for H 0 vary by 0.45σ depending on such assumptions. In our case the variations remains within less than 0.1σ because in each case the theoretical error already takes into account the uncertainties on these rates.…”

“…Previous data releases showed a tension between the BAO scale inferred from the BOSS galaxy survey and Lyman-α survey. However, in DR14, a substantial amount of additional data has reduced the tension between these surveys [30,32], such that combining all BAO measurements makes sense statistically, as recently pointed out by Cuceu et al [31]. The overlap between the BAOgalaxy + BBN and the BAO-Lyman-α + BBN preferred regions is small, and favors low values of H 0 in better agreement with Planck than with SH0ES [31].…”

“…In order to test our pipeline, we first run with the same assumptions as Cuceu et al [31]: we replace our full BBN likelihoods with a Gaussian prior on ω b taken from Cooke et al [45] (for the case with a theoretical determination of the nuclear rate d(p, γ) 3 He). The only remaining difference with reference [31] is the calculation of the comoving sound horizon: our BAO likelihood uses the value calculated by class instead of an analytic approximation. Nevertheless, our results agree very well with [31] (and also [30]), with a final prediction of H 0 = 67.5 ± 1.1 km/s/Mpc (68%C.L.)…”

“…Since the debate on the Hubble tension is often presented as a direct confrontation between CMB data and direct H 0 measurements, it is interesting to devise independent approaches providing estimates of H 0 . Several authors [27][28][29][30][31] have proposed such an approached based on combined BAO and BBN data.…”